1. Technical Field
The present invention relates to a sintered body and a method for producing a sintered body.
2. Related Art
In general, a sintered body made of an inorganic material is obtained as follows: a compact is formed from a raw powder (mixed powder) that is an admixture of an inorganic material powder and a binder by using various forming methods such as an injection molding method; after the compact is degreased at a temperature that is higher than a melting temperature of the binder and lower than a sintering temperature for the inorganic material so as to obtain a degreased body; and the degreased body obtained is sintered.
However, for example, the raw powder used in the injection molding method includes a relatively large quantity of binder in order to improve fluidity in the injection molding. For removing the binder, long periods of heat application is required, thereby causing issues such as decrease of production efficiency, and deformation of the compact during the heat treatment.
Further, when the binder in the compact is not sufficiently removed by the heat treatment and then the binder remaining is evaporated during sintering, an issue such as an occurrence of cracks in the sintered body may occur.
In order to solve such issue, JP-A-3-170624, for example, discloses a method for producing a sintered body. The method to obtain the sintered body is as follows: a compact including a raw powder that is an admixture of an inorganic material powder and a binder containing polyacetal is treated with heat in an atmosphere containing acid in the form of a gas or boron trifluoride so as to obtain a degreased body, and the degreased body is sintered.
In general, acid that is a deleterious substance and boron trifluoride that is a poisonous substance are harmful to humans, thereby taking a lot of troubles such as fully protective equipment for handling them.
Further, since acid and boron trifluoride have high metal solubility, materials having high corrosion resistivity need to be used for facilities, thereby causing a high cost.
Furthermore, since an atmosphere containing acid causes air pollution if it is released in the air after heat treatment, cost to prevent it is required.
In addition to the above, polyacetal reacts with an atmosphere containing acid, generating formaldehyde. Since formaldehyde is combustible and flammable, and further, carcinogenic and toxicant, it may cause danger of fire and explosion, and health damage to workers.
Alternatively, such method for producing a sintered body has been known that a compact formed from a raw powder that is an admixture of an inorganic material powder and a binder containing an aliphatic carbonic acid ester based resin is exposed to an atmosphere containing ozone so as to degrease the compact, and then sintering the obtained degreased body.
However, it has been found that even if degreasing is performed in the atmosphere containing ozone, the compact cannot be sufficiently degreased.
Further, since ozone is extremely oxidative, in a case where a metal powder is used as an inorganic material powder, the metal powder is disadvantageously oxidized.
Further, a high cost of a degreasing step is also regarded as an issue because ozone that is consumed in large amounts during degreasing is a very expensive gas.